1. Field of the Invention
The invention relates to a colorless and transparent, amorphously processable polyamide molding composition which is characterized by having good resistance to stress cracking in alcohols, esters, ketones and fuels, by resistance to boiling water and by a particular impact strength.
2. Discussion of the Background
Transparent polyamides which are resistant to boiling water are known. Thus, for example, amorphous transparent polyamides based on aromatic dicarboxylic acids such as isophthalic acid and/or terephthalic acid and aliphatic and/or cycloaliphatic diamines such as bis(4-amino-cyclohexyl)methane (i.e. para-amino cyclohexyl methane, hereinafter PACM) are described in EP-A 0 050 742, EP-A 0 069 700, U.S. Pat. No. 2,696,482, U.S. Pat. No. 3,597,400, U.S. Pat. No. 4,207,411 and U.S. Pat. No. 4,369,305.
Although polyamides having aromatic units are transparent, they are not completely colorless, but exhibit a pale yellow or beige color tinge, especially after processing. U.S. Pat. No. 2,512,606 and DE-A 20 34 541 describe transparent polyamides obtained from exclusively aliphatic and cycloaliphatic components.
Polyamides according to U.S. Pat. No. 2,512,606 comprise aliphatic dicarboxylic acids having 6-10 atoms and PACM having a trans,trans (herein after also t,t) content of less than 30%. These polyamides are not resistant to boiling water and solvents, and, like the other polyamides of the prior art, have an adequate resistance to stress cracking in, for example, alcohols, esters and ketones.
In many applications, however, transparent polyamides are in contact with these solvents in the liquid form or in an atmosphere enriched in these solvents, so that resistance to these media is absolutely essential.
Such applications are, for example, spectacle frames, apparatus inspection windows and covers or lamp covers.
DE-A 20 34 541, finally, describes polyamides based on PACM having a t,t content of 40-70% and 3-ethyl-1,10-decanedicarboxylic acid. In particular, in this specification, the following is stated on page 5, paragraph 2: "In our own experiments, it has been found that polyamides obtained from the above-mentioned diamine and dodecanedioic acid are cloudy".
Polyamides obtained from linear dicarboxylic acids and PACM having a 51% trans,trans content are described in Macromolecules, 4, 1971, page 347 et seq. As can be seen from Table I on page 348 shown there, however, these polyamides are crystalline and accordingly are not transparent.
The object of the present invention is to provide a colorless and transparent, amorphously processable polyamide molding composition which does not have the above-mentioned disadvantages of the prior art.
Surprisingly it has been found that a suitable polyamide and copolyamide molding composition based on linear, aliphatic dicarboxylic acids and bis(4-aminocyclohexyl)-methane can be prepared if the content of the trans,trans isomer in the diamine component and in the isomer mixture is not less than 35% by weight and not more than 60 mol %.